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Why do cartridge heaters seem to fail during startup—especially after a weekend?

April 26, 2017cartridge fail Heaters weekend

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Why do cartridge heaters seem to fail during startup—especially after a weekend?

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A. Cartridge heaters use MgO, (Magnesium Oxide) a white powdery substance as their electrical insulator. MgO is hygroscopic, and as such tends to absorb moisture from the air. When full voltage is applied to a cartridge heater with moisture laden MgO, it can cause voltage arcs to the sheath tripping circuit breakers, blowing fuses, and destroying heaters.